This invention relates to methods and apparatus for preparing dielectric films for integrated circuits, particularly carbon-doped oxide (CDO) dielectric films. More specifically, the invention employs modulated ultraviolet radiation to increase the hardness and modulus of the film. In preferred embodiments, the film shrinkage and dielectric constant are minimally affected.
Modern integrated circuit manufacturing requires advanced techniques for creating materials having low dielectric constants (low-k materials). Using low-k materials as the inter-metal and/or inter-layer dielectric in integrated circuits reduces the delay in signal propagation due to capacitive effects. The lower the dielectric constant of the dielectric film, the lower the capacitance of the dielectric and the lower the RC delay of the integrated circuit (IC).
Low k dielectrics are conventionally defined as those materials that have a dielectric constant lower than that of silicon dioxide, that is k<4. However, with ever increasing technology demands, present efforts are focused on developing low-k dielectric materials with k less than 2.5. Methods of obtaining these ultra low-k materials include doping silicon dioxide with carbon to create a carbon-doped oxide (CDO), or incorporating air voids within a low-k dielectric to create a porous dielectric material, or a combination of both (i.e., creating a CDO porous dielectric).
Although these approaches of doping and/or introducing air voids into the dielectric will reduce the dielectric constant of films, they can also have detrimental effects on quality of the films, in particular the mechanical strength of the films. Introducing carbon (e.g., methyl groups) or air voids into the dielectric will reduce the density of the film and thereby reduces the mechanical strength of the films. These less dense films may not withstand the mechanical stress of subsequently performed integrated circuit fabrication processes such as chemical mechanical polishing (CMP) and packaging. That is, the films may crack or become crushed internally. In addition, these films tend to poorly adhere to other materials and may delaminate at interfaces with adjacent layers when subjected to the mechanical forces produced by CMP and other fabrication processes.
What are needed therefore are methods of improving the mechanical strength and adhesive properties of low-k dielectric films without substantially deleteriously affecting the desired properties of the low-k films.